Endothelial function cannot be assessed by the reactive hyperemia following occlusion

Abstract

Reactive hyperemia (RH) and the post occlusive reactive hyperemia (PORH) are known to assess vascular function in vivo and referred as useful prognostic tools in vascular medicine. However, its translation to clinical practice is poor due to important unsolved inconsistencies. Our group has been studying the adaptive responses following RH. Here we clarify the involved mechanism, its impact on general hemodynamics and the significance of these responses. A convenience sample of fourteen healthy women (48.0 ± 8.0 y.o.) was selected, all being normotensive non-menopausal, with no signs of vascular impairment (normal ankle-brachial index and mean arterial pressure MAP), and with (self-reported) equivalent levels of physical activity. The study followed all principles of good clinical practice established for human research and was previously approved by the institutional Ethics Committee. The protocol included three phases—a baseline register (Phase I) during rest, giving place to the occlusion as part of the PORH maneuver challenge period (Phase II) with one minute, followed by a ten-minute recovery period (Phase III). PORH was performed on one randomly chosen upper limb, using the cuff of the TASK FORCE® platform for the continuous monitoring of blood pressure and hemodynamics. After baseline acquisition, the cuff was rapidly inflated with 200 mmHg to occlude the brachial artery for one minute. Then the cuff was rapidly deflated, and signals registered for recovery recordings. Perfusion was measured in both hands by laser Doppler flowmetry (3rd finger) with a Perimed5000 system. To confirm previous evidence regarding the mechanism(s) involved, we also accessed the RH impact(s) on the contralateral forearm skin circulation by functional imaging using a multi-scan photoptoacoustic tomography (PAT) (MSOT iThera system). The tissue hypoxia related to RH-PORH is referred to evoke a local vasodilation, such that hyperemia occurs following the cessation of occlusion. Thus, any reduction of this response has been associated to endothelial impairment. However, our studies have shown suffcient evidence of a centrally mediated reflex rather than a local response mediated by local vasodilators. In fact, LDF clearly detected significant perfusion reductions in both hands during and following occlusion, more pronounced in the challenged limb, while PAT confirmed similar changes in the superficial plexus on the contralateral forearm. Additionally of interest, no significant hemodynamical changes were found with PORH apart from MAP when comparing recovery with baseline periods. Our results clearly show that the physiological significance of RH or POHR reduction can no longer be regarded to solely represent “endothelial disfunction” but rather an expression of a global adaptive hemodynamical response, centrally mediated, that might originate essential endpoints also measurable in the contralateral limb, with clinical utility. This research was financed by national funds through FCT - Foundation for Science and Technology, I.P. (Portugal), under the [UIDB/04567/2020] and [UIDP/ 04567/2020] projects, and by COFAC/ALIES for the use of the photoacoustic instrument. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.